The flow of marine debris in the ocean causes extensive damage to coastal environments. It is considered important to understand the flow of marine debris in the Sea of Japan for environmental research purposes. The small size of most marine debris in the Sea of Japan means that marine debris cannot be confirmed directly, even when a high-spatial-resolution satellite image is used. Thus, in order to extract candidate pixels containing possible marine debris, pixels with spectra that differ from those of the surrounding ocean and the wave crests were identified. As a first step towards monitoring marine debris, a method for identifying marine debris floating on the Sea of Japan has been proposed that uses a histogram showing the distance from the regression line of the scatter diagram of satellite spectral bands.